Clock thermostat apparatus for controlling the temperature of a space and resetting the temperature for energy conservation during selected time periods is broadly old, as shown in the Carl G. Kronmiller U.S. Pat. No. 2,558,617, which issued June 26, 1951, wherein a cam member is used to reset the control point of the space temperature responsive means to a lower value to control the space temperature below a normal temperature during selected periods of time.
With such setback thermostats, there has always been a desire to vary the pickup time of the temperature conditioning apparatus at the end of the setback period to have the space temperature up to a normal temperature at a certain desired time. Various ways of accomplishing such have been used, such as a cam surface which is designed to vary the pickup time. Even more elaborate systems are used where the pickup time is adjusted by an outdoor temperature responsive element.
The present invention is concerned with a simple, less expensive apparatus for varying the pickup time as a function of the conditioning load which the building is experiencing. As the conditioning load increases, the space temperature will drop a greater amount from the normal temperature during the setback time period. A temperature responsive means responsive to the drop in the space temperature during the setback time is used to select the required pickup time needed to bring the space temperature back to normal at a desired time.
Specifically, an inside temperature responsive means is used for resetting the space temperature responsive control to the normal temperature. The resetting operation is started at different time periods depending upon the drop in the space temperature occurring during the setback time period .